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Sunday December 30, 2012 8:57 AM

Twenty years ago, Canadian researchers discovered that grapefruit interferes with the body’s
metabolism of certain drugs, including the immunosuppressant cyclosporine and at least one drug
used to treat high blood pressure.

The same group of scientists reported recently that the number of drugs that react adversely
with grapefruit has increased, from 17 to 43. The list includes cholesterol-lowering statins such
as Zocor and Lipitor and blood-pressure medications such as Nifediac and Afeditab.

Chemicals found in grapefruit change the way these medications are metabolized in the
gastrointestinal tract, dramatically increasing concentrations of the drug in the bloodstream.
Those chemicals, called furanocoumarins, are also present in other citrus fruits, including Seville
oranges — the kind often used to make marmalade — and limes and pomelos, according to the
study.

The amount of grapefruit that can set off a reaction varies from drug to drug, the study notes,
but in many cases, about 8 ounces of juice or a whole grapefruit “has sufficient potency to cause a
pertinent pharmacokinetic interaction.”

The drugs in question have three common traits: They’re all taken orally; they all have limited
bioavailability (only small percentages of the active drug make it into the bloodstream); and they
all interact in the GI tract with an enzyme called CYP3A4. The researchers have identified more
than 85 drugs that might interact with grapefruit, but some of these interactions are unlikely to
cause serious adverse effects.